Photolithography, which is a key manufacturing means of a semiconductor device or the like, has two required vital characteristics such as an increase in resolution and a securement of depth of focus, which are in relation against to each other. For example, it becomes obvious that a mere increase in a numerical aperture of a lens of an aligner and a mere reduction of a wavelength of an exposure light alone cannot improve practical resolution (monthly journal SEMICONDUCTOR WORLD 1990.12, OYO BUTURI (APPLIED PHYSICS), Vol. 60, No. 11 (1991), or the like).
Under these circumstances, phase shift lithography has been drawing attention as technology of the photolithography for a next generation. The phase shift lithography is a method for improving resolution of optical lithography by changing only a mask without changing an optical system, and a method for utilizing mutual interference of transmitting lights and significantly improving the resolution of the exposure lights by giving a phase difference between the exposure lights which transmit the mask (hereinafter, described as a phase shift mask) having a phase shift effect.
The phase shift mask is a mask simultaneously having light intensity information and phase information, and various types of the mask such as Levenson, auxiliary pattern, self-alignment (edge-enhancement), and the like are known. These phase shift masks have a more complicated structure and require higher level of technology with regard to manufacture than conventional photomasks having the light intensity information alone.
As one of the phase shift masks, a phase shift mask referred to as a so-called halftone phase shift mask has been recently developed. The halftone phase shift mask is provided with a semi-transmitting part simultaneously having two functions of shielding function to allow exposure light to be transmitted with intensity not substantially contributing to exposure, and a phase shift function to allow the phase of the light to be shifted (generally inverted). Therefore, a shielding film (referred to also as an opaque film in some cases) pattern and a phase shift pattern are not required to be separately formed, and a simple structure and easy manufacture are therefore achieved.
Here, a cross-sectional view of the halftone phase shift mask is shown in FIG. 3. In a halftone phase shift mask 5, a mask pattern is formed by a light transmitting part 2 and a light semi-transmitting part 3 on a transparent substrate 1. The light transmitting part functions to transmit the light of intensity substantially contributing to exposure, with the transparent substrate 1 exposed, and meanwhile the light semi-transmitting part functions to transmit the light of intensity not substantially contributing to exposure, having a light semi-transmitting film formed thereon to allow the phase of the transmitting light to be shifted. Furthermore, by a phase shift of the light that transmits the light semi-transmitting part 3, the phase of the light that transmits the light semi-transmitting part 3 and the phase of the light that transmits the light transmitting part 2 have a substantially inverted relationship. Then, lights passing near a boundary between the light semi-transmitting part 3 and the light transmitting part 2 and mutually detoured in the other's region by a diffraction phenomenon are canceled each other to set the light intensity to be approximately zero. The halftone phase shift mask is formed by improving contrast of the boundary, that is, the resolution of the boundary, by using the effect of setting the light intensity to be approximately zero.
Meanwhile, the light semi-transmitting part of the aforementioned halftone phase shift mask must have optimum values required for both of the light transmittance and phase shift amount. Furthermore, an inventor of the present invention previously filed an application relating to the phase shift mask capable of realizing the optimum values thus required by a single-layer light semi-transmitting part (U.S. Pat. No. 2,837,803, U.S. Pat. No. 2,966,369).
In the phase shift mask, the light semi-transmitting part is composed of a thin film made of metals such as molybdenum, tungsten, and the like, and silicon, oxygen and/or nitrogen as main components, which is a thin film made of molybdenum silicide, specifically, oxidized molybdenum and silicon (abbreviated as MoSiO), oxynitrided molybdenum and silicon (abbreviated as MoSiON), or nitrided molybdenum and silicon (abbreviated as MoSiN). These thin films are capable of controlling the transmittance by selecting an oxygen content or an oxygen and nitrogen content, and capable of controlling the phase shift amount by thickness of the thin film.
Not only in the phase shift mask but also in a general transfer mask, which means a transfer mask having a mask pattern on a substrate, the mask pattern is frequently made of a material containing silicon from a viewpoint of controllability of the shielding function of the mask pattern or workability of the mask pattern. In other words, in a mask blank as a member before patterning the transfer mask, a portion (a film) becoming the mask pattern is frequently formed by sputtering using a sputter target containing silicon. However, when the target containing silicon is used, there is a problem that many particles are generated during deposition. This is because that discharge is prone to be unstable during deposition using the target containing silicon. When the particles are generated during the deposition, mixture of the particles in the film occurs. When the particles come off from the film during cleaning or the like, a film thickness becomes thinner than an originally needed film thickness. For example, in the case of a shielding film, a shielding function cannot be exerted, depending on a degree of the film thickness becoming thin, resulting in a white defect, sometimes.
Furthermore, in the aforementioned halftone phase shift mask blank, a target containing a large silicon content is often used in order to control the transmittance of the light semi-transmitting part, thereby more remarkably posing the problem of generating particles when using the target containing silicon. Furthermore, when the particles are mixed in the light semi-transmitting film and come off from the film during cleaning or the like, the problem is more remarkably posed than the case of the aforementioned light shielding film. Specifically, in the case of the light semi-transmitting film, the phase shift amount or the transmittance changes according to a film thickness becoming thinner than the originally needed film thickness, thereby directly influencing the transfer characteristic. Therefore, if the generation of the particles when using the target containing silicon is reduced, this effectively works to reduce the defect of the phase shift mask.
When the phase shift mask blanks, which is a member before patterning, is provided having the light semi-transmitting part formed of the thin film as described above, the light semi-transmitting part formed of a single layer film of a single material can be obtained. According to the light semi-transmitting part thus formed, the deposition process can be more simplified and a single etching medium can be used, compared with a case of forming the light semi-transmitting part with a multi-layer film of different. materials. This contributes to simplifying a manufacturing process from the phase shift mask blank to the phase shift mask.
The thin film of MoSiO, MoSiON, or MoSiN is deposited by reactive sputtering in a gas atmosphere containing oxygen and/or nitrogen, using a target containing molybdenum and silicon. However, in accordance with micronization of the mask pattern, tolerance of a defect existing in the light semi-transmitting film of the phase shift mask blank has become extremely strict.
Furthermore, in the light semi-transmitting film, from a viewpoint of discharge stability during the deposition, from a viewpoint of advancement of the wavelength of the exposure light from KrF (248 nm) to ArF (193 nm), from a viewpoint of the transmittance of the light semi-transmitting film to be a high transmittance (9% to 20%), or the like, it has been difficult to control a phase difference and the transmittance by only controlling the oxygen and/or nitrogen content during the aforementioned reactive sputtering. Therefore, the phase difference and the transmittance are controlled by applying a target (hereinafter, described as silicon as a main component (silicon rich)) containing metals and silicon and containing a larger amount of silicon rather than stoichiometrically stable composition. Incidentally, the silicon as a main component in the present invention refers to silicon containing 70 atm % or more.
However, when the light semi-transmitting film is subjected to reactive sputtering to be deposited by using the aforementioned target composed mainly of silicon, a problem becomes obvious that a rate of generating defects caused by the particles in the light semi-transmitting film is increased by the particles generated during the deposition. The particles refer to fine particles having a diameter of, for example, 0.3 to 2 μm or more. When the particles are mixed in the light semi-transmitting film thus deposited, during a cleaning process conducted after the deposition, the particles come off from the light semi-transmitting film, and consequently, they become a pinhole or a half pin hole, as will be described later, or are remained in the light semi-transmitting film without being removed, resulting in a defect. The defect causes a generation of a lack of a pattern called a white defect during a manufacturing process of the phase shift mask by patterning the light semi-transmitting film.
Here, the pinhole is formed when the light semi-transmitting film is deposited, with the particles generated during deposition adhered on the substrate, and the particles thus adhered on the substrate come off from the light semi-transmitting film during the cleaning process, a recessed part is thereby generated on the surface of the light semi-transmitting film and the bottom of the recessed part reaches the substrate. Also, the half pin hole is formed when the particles are adhered on the substrate, with the deposition of the light semi-transmitting film on the substrate advanced to a certain extent, and the particles thus adhered on the substrate come off from the light semi-transmitting film during the cleaning process, the recessed part is generated on the surface of the light semi-transmitting film and the bottom of the recessed part does not reach the substrate.
As explained above, when the light semi-transmitting film is subjected to the reactive sputtering by using the target mainly composed of silicon, the problem specific to the target and the reactive sputtering is seemed to be the reason for causing the particles during deposition. Specifically, the target mainly composed of silicon to be used is not formed of a single compound, but is made in a mixed target formed of a simple substance (frequently including a silicon simple substance) and/or two or more of mixtures of a compound. The problem of uniformity in the composition or characteristics is involved in the mixed target, and therefore when the composition and characteristics are not uniform, discharge stability during the deposition cannot be obtained, causing the generation of the particles. Furthermore, during the reactive sputtering, oxygen and/or nitrogen is/are used in order to control the phase difference and the transmittance of the light semi-transmitting film. However, when using oxygen, the problem is that the discharge stability is reduced.
Furthermore, in the halftone phase shift mask, the phase shift mask and the phase shift mask blank described in Japanese Patent Laid-open No. Hei 7-128840 are known as an object of preventing leakage of the exposure light. FIG. 4 is a cross-sectional view of the phase shift mask described in Japanese Patent Laid-open No. Hei 7-128840. As shown in FIG. 4, the halftone phase shift mask described in this patent is formed by forming a semi-transmitting layer patterned by forming a transmitting part by removing a part of the film formed on the whole surface of the transparent substrate, and forming a light-shielding layer (referred to also as an opaque layer in some cases) on a main part excluding the vicinity of a boundary part between the semi-transmitting layer and the transmitting part. FIG. 5 is a halftone phase shift mask blank for manufacturing the halftone phase shift mask in FIG. 4.
When a shielding film (a shielding layer) is formed with the particles being mixed in the light semi-transmitting film (a translucent layer) during the formation of the halftone phase shift mask blank in FIG. 5, the white defect is generated in the light semi-transmitting film as described above when the particles come off during cleaning process after deposition, the particles come off involving the light shielding layer of an upper layer when coming off, and in some instances, the particles come off involving the light shielding layer in the peripheries of the particles, thereby involving the problem that the light shielding layer is excessively pealed. When the shielding layer is thus excessively peeled, the leakage of the exposure light cannot be prevented, causing transfer failure when transferred to a base to be transferred.
Furthermore, with the advancement of transfer accuracy, an attempt is made to set the transmittance of the light semi-transmitting part of the half tone phase shift mask to be high (9% to 20%). When the particles are mixed in the light semi-transmitting film of the mask, the problem is that even a minute defect of such extent that causes no problem in a normal mask becomes a defect. When the particles mixed in the light semi-transmitting part come off during the cleaning process, the problem is that the transmittance of a defect part is diminished only to contribute to exposure. Furthermore, in such a mask, the light semi-transmitting part exhibits a high transmittance, thereby necessitating the light shielding layer provided thereon as shown in FIG. 4, and as described above, the problem caused by the excessive peeling of the light shielding layer is thereby generated.
The present invention is provided in consideration of the aforementioned problems, and an object of the present invention is to provide a method for manufacturing the high quality phase shift mask blank capable of manufacturing with a high yield with a rate of generating defects in the light semi-transmitting film set to be less than or equal to a desired value, a method for manufacturing the phase shift mask manufactured by patterning the light semi-transmitting film of the phase shift mask blank, and the sputtering target for manufacturing the phase shift mask blank.